High-uranium (U) coal is the dominant form of coal in Southwestern China. However, directly utilizing this resource can also harm the environment because this element is radioactive; it is, therefore, necessary to clean this kind of coal before burning. This research studied the geochemistry of toxic elements and their partitioning during the preparation of high-U coal in China. The results show that high-U coals are mainly distributed in Southwestern China and are characterized by a high organic sulfur (S) content and vanadium (V)-chromium (Cr)-molybdenum (Mo)-U element assemblage. These elements are well-correlated with one another, but are all negatively related to ash yield, indicating that all four are syngenetic in origin and associated with organic materials. A mineralogical analysis shows that U in Ganhe and Rongyang coal occurs within fine-grained anatase, clay minerals, guadarramite, and pyrite, while V occurs in clay minerals, pyrite, and dolomite, and Cr occurs in dolomite. Other elements, such as fluorine (F), lead (Pb), selenium (Se), and mercury (Hg), mainly occur in pyrite. By applying a gravity separation method to separate minerals from coal, the content of the enrichment element assemblage of V-Cr-Mo-U in Rongyang coal is still shown to be higher than, or close to, that of the original feed because this element assemblage is derived from hydrothermal fluids during syngenetic or early diagenetic phases, but other elements (beryllium [Be], F, manganese [Mn], zinc [Zn], Pb, arsenic [As], Se, Hg) can be efficiently removed. Once cleaned, the coal obtained by gravity separation was subject to a flotation test to separate minerals; these results indicate that while a portion of V and Cr can be removed, Mo and U remain difficult to extract. It is evident that the two most commonly utilized industrialized coal preparation methods, gravity separation and flotation, cannot effectively remove U from coal where this element occurs in large proportions. Finally, dilute hydrochloric acid (HCl) leaching experiments show that the majority of Mo and a portion of V, Cr, and U are adsorbed in clay minerals and organic matter and, therefore, exist in an adsorbed state. In this state, these elements can be removed using the acid method. Thus, as U cannot be fully removed from coal, the use of high-U coals is not recommended.

The occurrence characteristics of sodium and its potential relationship with macerals in Zhundong coal, as well as in Shenfu coal with average sodium levels, are investigated in this study. A new five-step sequential extraction method was first conducted for determination. The occurrence status of sodium and its related macerals in samples was determined by microscope and SEM–EDS (scanning electron microscope–energy dispersive X-ray spectroscopy). Soluble sodium salts (H₂O-Na) make up the primary proportion of sodium in Zhundong coal, at approximately 50%, while various sodium species are distributed in Shenfu coal with nonobvious differences. Inertinite contains more sodium than vitrinite does in both coals, and the highest enrichment degree of sodium was discovered in inertinite from Zhundong coal, which presented primarily as NaCl crystals (H₂O-Na) in fusinite cells, with a local weight percentage of over 15%. More specifically, H₂O-Na and insoluble Na both tend to enrich in fusinite. Additionally, it is found that maceral-rich products can be gathered using triboelectrostatic separation, and a portion of sodium can thus be removed from the coal by removing inertinite. This study may provide new insights and references regarding sodium removal from Zhundong coal.

During the Late Permian period, the coal from the Jiashun Mine in Xingren City, Guizhou Province, China, is characterized by a high sulfur (5.84%) and lithium (Li) (94.5 μg/g) content. Lithium is a critical metal in the context of global energy transition. Considering the importance of environmental protection and resource utilization, the mode of occurrence and distribution of trace elements in different coal preparation products were investigated. The obtained results indicated the following: (1) The minerals in Jiashun coal were mainly composed of veined and epigenetic pyrite, quartz, and kaolinite. Most of the minerals could be effectively removed from the cleaned coal through gravity separation. (2) The mode of occurrence of rare earth elements and yttrium (REY) in the coal was relatively complex, and they were mainly found in middlings from gravity separation and in flotation tailings. (3) The mode of occurrence of the trace elements in the coal significantly influenced their removal rate. The removal rate was significantly higher for trace elements removed through gravity separation compared to those removed using flotation. The trace elements mainly found in fine-grained minerals wrapped by organic matter or combined with organic portions had better removal results through flotation. The trace elements that occurred both in the minerals and organic matters had low removal rates (<25%) using two coal preparation methods. (4) Li was more enriched in the middlings from gravity separation (98 μg/g) and in flotation tailings (102 μg/g), reaching the marginal grade (80 μg/g) of Li in coal. (5) Li in Jiashun coal may be derived from intermediate-felsic rocks at the top of the Kangdian Upland and late hydrothermal solutions.

The severe slagging caused by high-alkali coals restricts the utilization of Xinjiang coal resources in China. This study investigates the mineral composition, geochemical characteristics, modes of occurrence, and controlling factors of alkali and alkaline earth metals in high-alkali coals from the Dananhu Coalfield, Turpan–Hami Basin. The investigated coals are classified as lignite, characterized by low ash yield, extra low sulfur, and medium–high alkali contents. Quartz and kaolinite are dominant, with accessory calcite, K-feldspar, pyrite, gypsum, siderite, celestite, and Ba-bearing celestite. Compared to average Chinese coals, Na, Mg, Ca, and Cl are enriched, with the shallowest No. 3 coal seam showing the highest enrichment. Based on the correlation analysis, K is likely associated with K-bearing aluminosilicates (e.g., K-feldspar and illite), while Ca, Mg, and Na probably exhibit both organic and inorganic affinities. Sequential extraction results indicate that Na is predominantly water-soluble and ion-exchangeable, whereas Ca and Mg are largely ion-exchangeable and HCl-soluble. The abundant cell cavities and oxygen-containing functional groups in lignite provide both binding sites and accommodation space for Ca, Mg, and Na. Despite a continental freshwater depositional setting, tectonic isolation and persistent arid conditions potentially promoted epigenetic enrichment of Na, Mg, and Ca. Closed hydrogeological units formed by tectonic movements restricted leaching and enhanced evaporation, concentrating these elements in the coal seams. Future research should focus on implementing economically feasible dealkalization pretreatment processes for the clean utilization of high-alkali coals.

Relevance. Russian coal exports have been steadily increasing in recent years, and Far Eastern ports, originally not adapted to dusty cargoes, have switched to coal operations. Unoptimized coal handling leads to increased content of coal-containing particles in the air and to various environmental problems. Aim. To analyze the concentration of particulate matter in the air and the chemical composition of particles on the surface of conifer needles in the Posyet settlement (Primorsky Krai, Russia), where a large coal terminal operates. Materials and methods. The chemical composition was studied on the surface of conifer needles by X-ray fluorescence and in washout of conifer needle samples using Raman spectroscopy and energy dispersive analysis. Concentrations of particles with the diameter of 2.5 and 10 μm (PM2.5 and PM10, respectively) were measured using automatic monitoring stations. Results and conclusions. Chemical composition was dominated by mineral particles (calcite, silicates, etc.). However, the presence of coal particles (up to 8.3%) and metal particles was also observed. Mean concentrations of PM2.5 and PM10 were within the Russian and international health standards, but close to their upper limits. Concentrations of both measured particle fractions were highest during the winter months (as well as in March, which is traditionally a cold month in the Far East), followed by a gradual decrease. The study obtained new data on the annual variations of concentrations of PM2.5 and PM10, as well as on the basic composition of particles from the surface of woody vegetation (needles) as an indicator of the state of air pollution in this settlement.

Coal can enrich hazardous trace elements in specific depositional environments, and their distribution and modes of occurrence are controlled by multiple geological factors. This study investigated the geochemistry of hazardous trace elements in the Middle Jurassic Xishanyao Formation coals of the Piliqing Open-Pit Mine, Yili Coalfield, using proximate, mineralogical (XRD, SEM-EDS), and geochemical (ICP-MS, carbonate C-O isotope) analyses. The coals were ultra-low-ash and low-sulfur subbituminous, with a whole-coal weighted-average CaO content of 1.95%. Most hazardous trace elements were not enriched relative to world coal averages: F, Cr, Ni, Co, As, Sr, and Th were near global values; whereas Se, Cd, Mo, Tl, Pb, U, and Hg were depleted. Vertically, F, V, Cr, Hg, Pb, Tl, Th, and U were higher in the roof and floor strata than in the coal seams, indicating terrigenous detrital input as the primary control, whereas Sr was governed by carbonate and aluminosilicate minerals. The only pronounced enrichment was the anomalously high V (212 μg/g) in sample C407, which possibly recorded locally reducing conditions at the base of the No. 4 seam; however, this single-sample observation precludes a firm syngenetic interpretation. Carbonate C-O isotopes showed that the calcite veins precipitated from coal-altering epigenetic hydrothermal fluids that carried an admixed organic-matter-derived carbon component. These fluids delivered mainly Ca, Mn, and Sr, without adding harmful elements to the coal. This signature reflects a dominantly syngenetic geochemical pattern that was locally overprinted by non-oxidizing hydrothermal fluids, in which weakly oxidizing, shallow-water conditions were unfavorable for the reducing enrichment of U, Mo, Re, and Se. In contrast to the coal-hosted uranium deposits of the Southern Yili Basin margin, Piliqing coals showed no evidence of post-depositional oxidized-fluid infiltration, indicating limited environmental risk.